Device comprising a magnetron tube



Oct. 10, 1950 K. POSTHUMUS 2,525,721

DEVICE COMPRISING A MAGNETRON TUBE Filed May 1, 1946 TUNED CIRCUIT TUNED CiRCUIT KLAAS P05 TH UM US.

INVENTOR.

g) QKU JQ AGENI Patented Oct. 10, 1950 UNITED STATES PATENT OFFICE DEVICE COMPRISING A MAGNETRON TUBE Klaas Posthumus, Eindhoven, Netherlands, as-

signor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford,

Conn, as trustee Application May 1, 1946, Serial No. 666,240 In the Netherlands February 27, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires February 27, 1962 6 Claims. (Cl. 315-) This invention relates to a device comprising a magnetron tube, the vacuous envelope of the tube being made of insulating material. Such devices are used, among other things, for producing electrical oscillations of ultra-high frequency.

In practice such devices entail the drawback that the frequency of the oscillations produced by the tube exhibits excessive variations, for

example due to variations in the supply voltages or due to modulation voltages, or both.

If a tuned circuit is connected in parallel with a magnetron tube and the damping of the circuit is sufficiently small, oscillations will be produced of which the frequency approaches the resonance frequency of the circuit.

The frequency of the. generated oscillations is, however, also determined by the construction of the tube and by the operating voltages so that, if the operating conditions vary, for example due to variations in the supply voltages, the frequency of the produced oscillations also undergoes a variation.

According as the damping of the tuned circuit is lower and the resonance curve thereof is sharper, the variations in the frequency ultimately produced are smaller, while the frequency-determining action of the circuit is stronger, according as thecircuit is coupled more tightly with the output electrodes of the tube.

The present invention has for its purpose to provide means whereby in a device of the said kind a circuit having a very low damping such, for example, as a cavity resonator, may be used as a frequency-determining impedance and this in such manner that a maximum coupling exists betweenthe circuit and the output electrode, no additional damping being brought about by connecting leads and the like.

According to the invention, this object is attained by that a device comprising a magnetron tube, in which the vacuous envelope of the tube is made from insulating material, utilises a tube in which the anode or the anode parts does not surround or do not surround the cathode completely, at least two electrodes connected to an impedance being arranged outside the envelope of the tube at places where the cathode is not surrounded by the said anode or anode parts.

According to the invention, the device is preferably so constructed that the electrodes arranged outside the envelope form part of a tuned circuit, for exampleof a cavity resonator.

The invention will be more clearly understood byreference of the accompanying drawing shou= anode plates;

ing, by way of example, several embodiments thereof.

Figure l is a diagrammatic and transverse sectional view of a tube having one anode;

Fig. 2 is a similar view of a tube having two Fig. 3 is a transverse sectional view of a modified form of the invention;

Fig. 3a is a longitudinal sectional view of the tube shown in Fig. 3 and shows the magneticfield producer;

.Fig. 4a is aperspective viewof another form. of cavity resonator;

Fig. 4b is a transverse sectional view of an degice including the. cavity resonator of Fig, 4a; an

Fig. 4c is a diagram of the circuit of a con-- ventionalprior art cavity resonator.

Fig. 1 is a sectional view of a magnetron'tube l accordingto a plane normal to .the cathode 2; An anode 41s arranged inside and parallel to the insulating envelope 3, which may be for example of glass, said anode constituting part of a cylindrical. surface which is substantially co-axial of the cathode 2. However, this anode does not surround the cathode completely and at places where the cathode is not surrounded by it twoelectrodes 6 and l are arranged in the .immediate vicinity of the outside of the glass wall and parallel thereto. 2

Due to a battery 8 included in the connecting line between the anode 4 and the cathode, said anode has a positive voltage relatively to the cathode. The two electrodes 6 and l are 6011-. nected to a tuned circuit 9 which is earthed in a point of symmetry 10.

It is assumed that a magnetic field of usual strength and substantially parallel to the cathode is present. The operation of the device is substantially the same as that of known magnetron circuits and may be briefly described as follows:

Under the co-operation of the electric field which exists between the cathode and the anode and the magnetic field of which the lines of force are substantially normal to the electrical lines of force, the electrons emitted by the cathode upon heating will move in paths round the cathode and, if at the electrodesyfi and I a,high-. frequency alternating voltage of suitable frequency is present, divide into. groups due to the high-frequency fields which exist in thegaps between the 'electrodes l, S and "l.

If the phase relations are correct, the groups of electrons .thus produced will give an energy to the electrodes 6 and?! asa'result of induce tion, so that the original voltages set up at the electrodes 6 and 7 are amplified and the tube thus operates as a generator.

For this purpose it is necessary, as is wellknown, that a definite relation should exist between the electric and the magnetic field intensity on the one hand and the frequency to which the circuit 9 is tuned on the other hand. Due to the cession of energy, the electrons are retarded so that at last they impinge on the anode 4 which serves as a collecting electrode.

A similar circuit is shown in Fig. 2, the envelope, however, containing two anode parts 4 and 5 and one electrode arranged outside the envelope being always located between two anode parts arranged inside the envelope. The operation of this device is for the rest similar to that of the embodiment illustrated in Fig. 1 and consequentl needs no further explanation.

In the known devices. comprising a magnetron tube use must be made of conductors connecting the tuned circuit 9 to the electrodes from which the high-frequency energy is derived, said conductors having to be led through the glass wall of the tube.

The impedance of these conductors has the effect of diminishing the coupling between the circuit 9 and the output electrode of the tube, while the losses of such conductors led through glass, which are considerable in particular for high frequencies, bring about an appreciable damping of the tuned circuit, due to which the frequency stability of the circuit is detrimentally affected. In a-device according to the invention, however, the conductors which connect the tuned circuit to the energy abstracting electrodes are not led through the glass wall so that the said losses do not occur. Moreover, the diameter of the wire of these leads may be chosen at will so that the frequency stability is determined almost solely by the properties of the circuit.

A highly suitable form of construction of a device according to the invention, in which the connecting leads are completely omitted, is shown diagrammatically in Fig. 3, the electrodes arranged outside the envelope forming part of a tuned cavity resonator ll. Such a cavity resonator has a very low damping and consequently a very high degree of frequency stability. Since connecting leads need not be used, the favorable properties of such a cavity resonator come fully to advantage. The high-frequency energy may be derived from the circuit in known manner by means of a transmission line 53 ending in a loop I2. A' voltage which is positive relatively to the cathode 2 may be supplied to the anode parts 4 and 5 through an opening in the cavity resonator.

Figs. 4a and 4b represent another form of construction of a device according to the invention, the electrodes arranged outside the envelope forming part of a cavit resonator. The circuit according to this form of construction substantially corresponds to the known circuit shown in Fig. 40, but differ therefrom in that the four anode parts 4, 4', 5 and 5 do not surround the cathode completely and that at places where the cathode is not surrounded there are arranged electrodes outside the tube, that is the electrodes 6, 6 and i, 1'. In Fig. 4c the anode parts are connected to a tuned circuit 9 in such manner that any of the anode parts has a high-frequency voltage of opposite sign relatively to the adjacent anode parts.

In the form of construction according to the invention the four electrodes 6, 6', 7 and i located 4 outside the tube are connected to a cavity resonator l2 and this in such manner that upon energising the cavity resonator a high-frequency voltage of opposite sign is set up at adjacent electrodes.

As is shown in Fig. 4a, the cavity resonator [2 has the form of a hollow cylinder of which the top surface and the bottom surface have fastened to them respectively two electrodes 6, l and 6, I which are located radially relatively to each other in such manner that the spacings between the strips are equal. Fig. 4b shows the arrangement of the magnetron tube relatively to the cavity resonator in a section normal to the axis of the cylinder. The magnetron tube contains four anode parts 4, 4', 5 and 5 which do not surround the cathode completely, while the cavity resonator I2 is arranged relatively to the tube in such manner that the electrodes 6, 6', 1 and 1' are located at places where the said anode parts do not surround the cathode.

Since the voltages set up at the top surface and the bottom surface of the cavity resonator [2 are always in counterphase, this is also the case with voltages set up at the pairs of electrodes 6, 1 and 6, I. Like the electrodes 8 and I, the electrodes 6 and l are always of equal phase so that the circuit indeed substantially corresponds to that shown in Fig. 40.

In the form of construction shown, the anode parts arranged inside the tube, which have supplied to them a positive voltage relatively to the cathode, substantially have no high-frequency alternating voltage. However, the circuit may be modified in such manner that these anode parts have also connected between them an impedance, so that a high-frequency voltage is set up be tween the anode parts. In this case the tuned circuit connected to the electrodes arranged outside the tube will remain frequency-determining, since no connection leads are present between these electrodes and the tuned circuit, so that a tight coupling free from losses with the tuned circuit occurs, which is not the case with the electrodes located inside the tube.

A device according to the invention connected in this manner may be used for frequency transformation by providing for the tuned circuit which is connected to the electrodes arranged outside the tube to be tuned to the double frequency of the tuned circuit which is connected to the anode parts arranged inside the tube.

It is for the rest evident that the device according to the invention may also be used for amplifying ultra-high frequency oscillations, while, if the necessity arises, the number of anode parts arranged inside the tube and the number of elec trodes arranged outside the tube may still be increased.

I claim: a

1. A device comprising a magnetron tube having an evacuated envelope of insulating material containing a cathode and anode means consisting of arcuate sections disposed arcuately in spaced relation around the cathode but not completely surrounding the cathode, electrode means around the outside of the envelope and comprising a pair of members with the-members dis posed at places where the cathode isnot surrounded by sections of the anode means, and an impedance connected to said electrode means.

2. A de ice as claimed in claim 1, in which the number of electrodes outside the envelope is equal to the number of anode parts inside the envelope, one electrode being outside the envelope between any two adjacent anode parts inside the envelope.

3. A device as claimed in claim 2, in which the electrodes outside the envelope form part of a tuned circuit, for example of a cavity resonator.

4. A cavity resonator device comprising a closed vessel containing an anode, a cathode as a source of electrons and means connected to said anode and said cathode for establishing an electric field to act upon the electrons in a predetermined direction, means disposed around the vessel to establish a magnetic field to act upon the electrons in a direction transverse to said predetermined direction, and means constituting resonator plates disposed outside the vessel adjacent regions in the vessel that are relatively free of the electric field within the vessel whereby said means will have voltages induced therein by electrons caused to move adjacent to said means, and impedance means connected to said resonator plates.

5. A cavity resonator device comprising an inner closed and evacuated vessel containing a cen-- tral cathode as a source of electrons and arcuate- 1y disposed anode means surrounding said cathode for establishing electric field zones spaced by relatively field-free regions, and an outer closed vessel surrounding the inner vessel and embodying arcuately shaped elements disposed outside of the inner vessel and adjacent the field-free zones in the inner vessel, and an electrically tuned system connected to, the arcuately shaped elements disposed outside of the inner vessel.

6. A cavity resonator device comprising an inner closed and evacuated vessel containing a central cathode as a source of electrons and arcuately disposed anode means surrounding said cathode for establishing electric field zones spaced by relatively field-free regions, and an outer closed vessel surrounding the inner vessel and embodying arcuately shaped elements disposed outside of the inner vessel and adjacent the field-free zones in the inner vessel, and an electrically tuned system electrically coupled to the arcuately shaped elements of the outer vessel for conducting energy to an external circuit.

' KLAAS POS'IHUMUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,166,210 Fritz July 18, 1939 2,173,252 Fritz Sept. 19, 1939 FOREIGN PATENTS Number Country Date 345,589 Italy Jan. 11, 1937 445,084 Great Britain Apr. 2, 1936 

